so as a guy that did smoke in the 70's (mostly mexican, we could get a 4 finger lid for 10 bucks back then) - I relate this little story that I (surprisingly, considering) remember quite well.
One of our go-to's were what we called Sherman sticks - they were really cheap, even for back then, I think they were 50 cents? (I could get a hit of dragon blotter - for those that know what that is - for 2 bucks). They were basically some sort of english cigarette - I think in brown paper? and they had this weird chemical smell to them - but man, you took one or two hits of that thing, boom with a capital B - you (or at least I) was sitting down for a couple of hours. Now this from a guy that's done peyote, mushrooms, blotter, microdot, etc. This stuff was bad. But none of us - at least that I know of - knew what it was.
So fast forward, 25 years or so, and I'm working advertising sales and I've got a customer that owns a funeral home - and he's showing me around the place (thats another story) and I smell something familiar - I'm trying to place it - and damn - sure enough it's that same chemical smell from the shermans we used to smoke. I tell him the connection, and he tells me it's formaldehyde - that he has to keep it locked up special because the druggies in the neighborhood try to steal it.
I remember back in the day they used to say we were killing brain cells with all the drugs we were using - turns out, we were actually preserving them.